Prior to beginning a course of radiotherapy, a plan for the treatment is generated. The aim of the treatment plan is to establish how to apply the radiotherapy to the patient so that the target region receives the desired, therapeutic dose, whilst the surrounding healthy tissue receives as little dose as possible.
The process of treatment planning is complex and time-consuming. It involves first acquiring an image of the patient (“the planning image”) which contains at least the region which is targeted for treatment as well as the surrounding area. A clinician reviews the image and specifies maximum and minimum doses for different regions shown in the image. For example, the target region may be assigned a minimum dose (i.e. the target region should receive a dose of at least X), while sensitive healthy regions near the target region may be assigned a maximum dose (i.e. this sensitive region should receive a dose of no more than Y). This three-dimensional map is then used to generate a treatment plan which specifies the dose to be administered to the patient and the angle at which that dose is to be applied from. Typically each treatment plan will consist of multiple doses from multiple directions, or “arcs”.
The generation of the treatment plan can be expressed as a mathematical problem in which the overall dose to healthy tissue must be minimized, subject to constraints as to the maximum dose to be delivered to sensitive regions (such as healthy organs, for example) and the minimum dose to be delivered to target regions. Although complex, the problem can be solved using significant computing resources and one of various techniques known to those skilled in the art.
The treatment plan so generated does not always produce an optimal clinical outcome. Therefore, every treatment plan is reviewed by a clinician to check that it delivers an acceptable dose profile to the patient. If not, a further iteration of the process receives the feedback from the clinician and generates an updated treatment plan. This process can be repeated as many times as necessary until an acceptable treatment plan is created.
The treatment plan is then passed to the radiotherapy system to be implemented, delivering targeted radiation to a patient in order to treat some medical condition. The treatment plan merely specifies the dosage to be delivered to the patient and the direction the dosage is to be applied from, however. Although useful from a clinical point of view, such information does not specify the voltage to be applied in the linear accelerator to generate the therapeutic radiation; it does not specify the length of time power should be supplied to the rotatable gantry in order to move the radiation head through a certain range. In short, it does not specify the actual instructions to be input to the radiotherapy system to put the treatment plan into effect. In order to translate the information in the treatment plan into useful instructions for the various components of the system (and there are many such components), the radiotherapy system requires a calibration data set which converts the treatment plan dosage instructions into practical instructions for the components.
The calibration data set is generally stored locally to the radiotherapy system, and may be amended over time to account for changes to the radiotherapy system itself. Components of the system may be upgraded, or new components added (e.g. new collimation apparatus). Conversely, the performance of existing components may degrade over time. By appropriate maintenance of the calibration settings for these components, the performance of the system as a whole can be maintained at a consistent level over a prolonged period of time.
As noted above, the calibration data sets for radiotherapy systems are typically stored locally. Furthermore, they are also generally updated manually. For example, a technician may review and update the calibration data set as part of a regular maintenance schedule. Additionally, or alternatively, the technician may update the calibration data set only when some maintenance is carried out on the system (e.g. installation or replacement of system components).
This manual entry of calibration data can lead to problems. For example, if the calibration data set contains an error (e.g. through a typographic or otherwise erroneous entry of data), the treatment delivered to the patient may not conform to the dosage profile that was predicted when the treatment plan was generated and approved by a clinician. At the same time, however, it is beneficial to allow a degree of flexibility to the technicians maintaining the calibration data sets, to allow radiotherapy systems to be operated for longer and otherwise to account for minor variations between each system.